Method for determining focus deviation amount in pattern exposure and pattern exposure method

ABSTRACT

A plurality of first measurement patterns each including a protruding pattern formed of a resist film and a recessed pattern having a space with a shape corresponding to the protruding pattern are formed on a first substrate such that they have different focus values at a time of exposure, edge inclination amounts of the plurality of first measurement patterns are measured, and a focus dependence ( 17 ) of the edge inclination amounts is obtained based on correspondences ( 7 ) and ( 14 ) between the edge inclination amounts and the focus values. A second measurement pattern including the protruding pattern and the recessed pattern is formed on a second substrate so as to measure edge inclination amounts of the second measurement pattern, and a focus deviation amount deviating from a best focus at the time of exposure of the second measurement pattern is calculated from the edge inclination amounts of the second measurement pattern based on the focus dependence of the edge inclination amounts. A dimension of the protruding pattern and a dimension of the space of the recessed pattern are set to be different so that best focus values at the time of exposing the protruding pattern and the recessed pattern become closer.

TECHNICAL FIELD

The present invention relates to a method for determining a focusdeviation amount in pattern exposure with respect to a resist film.Also, the present invention relates to a method for extracting the focusdependence of an edge inclination amount of a pattern used for thatdetermining method. Further, the present invention relates to a methodfor carrying out a pattern exposure with respect to a resist film whileperforming a focus correction.

BACKGROUND ART

When forming a minute resist pattern on a resist film on a semiconductorwafer by lithography, the focus position at the time of pattern exposuregreatly influences the dimensional accuracy of the resist pattern. Thus,at the start of construction of a new process, wafers printed withpatterns by changing focus values of exposing equipment are produced perunit exposure, and the dimension of the formed resist patterns ismeasured, thus setting the best focus value for obtaining apredetermined pattern dimension.

However, because of various process variations, it is unlikely that thebest focus value that has been set can be used forever to obtain theresist pattern with a predetermined dimension. Therefore, in aconventional technology, a focus deviation has been corrected accordingto the variation in an optimal position of focusing caused by theprocess variation. For doing this, it is necessary to determine thefocus deviation amount deviating from the optimal position. JP2003-59813 A describes a method for determining such a focus deviationamount. This method will be explained with reference to FIGS. 19A, 19B,20A, 20B and 21.

FIG. 19A shows a cross-section of a line pattern 1 formed of a resistremaining in a linear form. FIG. 19B shows a cross-section of a spacepattern 2 having a space 3 that remains after removing a resistpartially in a linear form. These resist patterns are used for observinghow the shape of the formed patterns varies when shifting a focus at thetime of pattern exposure using a mask in a positive direction and anegative direction from a best focus value. Here, the positive side ofthe focus value refers to a state in which a focus is achieved on a sidebelow the best focal point, and the negative side of the focus valuerefers to a state in which a focus is achieved on a side above the bestfocal point.

The variation in the shape of the line pattern 1 and the space pattern 2described above with respect to the focus variation becomes notable inthe inclination amount of end faces of the pattern (in the following,referred to as an edge inclination amount). Now, EW1 denotes the edgeinclination amount of the line pattern 1 shown in FIG. 19A, and EW2denotes that of the space pattern 2 shown in FIG. 19B. With theirhorizontal axes indicating the focus value and their vertical axesindicating the edge inclination amounts EW1 and EW2, FIGS. 20A and 20Bshow lines indicating the focus dependence of the edge inclinationamount, namely, a variation in the edge inclination amount with respectto the variation in the focus value. Each line corresponds to ameasurement result obtained by each of exposures with different exposureamounts. The focus value 0 corresponds to the best focus.

As shown in FIG. 20A, the edge inclination amount EW1 of the linepattern varies notably when the focus is shifted from the best focalpoint in the negative direction. On the other hand, as shown in FIG.20B, the edge inclination amount EW2 of the space pattern hardly varieswhen the focus is shifted from the best focal point in the negativedirection but varies notably when the focus is shifted to the positiveside. From these edge inclination amounts EW1 and EW2, a model showing afocus dependence of the edge inclination amount can be formulated asshown in FIG. 21. In other words, by obtaining the difference betweenEW1, which varies on the negative side, and EW2, which varies on thepositive side, i.e., EW1—EW2, it is possible to obtain a curve showingthe characteristics of the variation in the edge inclination amount withrespect to the variation in the focus value. Using this curve, a focusdeviation amount can be determined from the correspondence with the edgeinclination amount.

However, as becomes clear from FIG. 21, there is a region in which thevalue of the vertical axis (EW1−EW2) remains flat near the best focusvalue (=0 μm). Thus, with this method, the focus deviation amount cannotbe determined accurately near the best focus value.

The formation of this flat region is attributable to two factors. First,the resolutions of the line pattern and the space pattern are differentin the current resist. Usually, the focus is achieved on the linepattern, but this causes the space pattern to be out of focus. In otherwords, the best focus values of the line pattern and the space patterndo not match. For example, the best focus value of a 0.18 μm linepattern does not match with that of a 0.18 μm space pattern.

Second, there is a dimensional error in manufacturing masks. In afactory where plural types of products are produced, masks aremanufactured for each type. When manufacturing plural kinds of masks,dimensional errors occur inevitably. Such dimensional errors of themasks result in a problem that the best focus values of the line patternand the space pattern do not match.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a method fordetermining a focus deviation amount capable of detecting accurately thedeviation amount of a focus from a desired position in pattern exposurewith respect to a resist film. It is another object of the presentinvention to provide an exposure method conducted while correcting afocus position using this determining method.

A method for determining a focus deviation amount according to thepresent invention includes forming on a first substrate a plurality offirst measurement patterns, each including a protruding pattern with apredetermined shape formed of a resist film and a recessed patternhaving a space with a shape corresponding to the protruding pattern, theplurality of first measurement patterns having different focus values ata time of exposure, measuring edge inclination amounts of the protrudingpattern and the recessed pattern in the plurality of first measurementpatterns, obtaining a focus dependence of the edge inclination amounts,which is a characteristic showing how the edge inclination amounts varywith respect to a variation in the focus value at the time of exposure,based on correspondences between the measured edge inclination amountsand the focus values, forming on a second substrate a second measurementpattern including the protruding pattern and the recessed pattern so asto measure edge inclination amounts of the protruding pattern and therecessed pattern in the second measurement pattern, and calculating afocus deviation amount deviating from a best focus at the time ofexposure of the second measurement pattern from the edge inclinationamounts measured with respect to the second measurement pattern based onthe focus dependence of the edge inclination amounts. A dimension of theprotruding pattern and a dimension of the space of the recessed patternare set to be different so that best focus values at the time ofexposing the protruding pattern and the recessed pattern become closer.

A method for extracting a focus dependence of an edge inclination amountaccording to the present invention includes forming on a substrate aplurality of measurement patterns, each including a protruding patternwith a predetermined shape formed of a resist film and a recessedpattern having a space with a shape corresponding to the protrudingpattern, the plurality of measurement patterns having different focusvalues at a time of exposure, measuring edge inclination amounts of theprotruding pattern and the recessed pattern in the plurality ofmeasurement patterns, and obtaining a focus dependence of the edgeinclination amounts, which is a characteristic showing how the edgeinclination amounts vary with respect to a variation in the focus valueat the time of exposure, based on correspondences between the measurededge inclination amounts and the focus values. A dimension of theprotruding pattern and a dimension of the space of the recessed patternare set to be different so that best focus values at the time ofexposing the protruding pattern and the recessed pattern become closer.

A pattern exposure method according to the present invention includesforming on a first substrate a plurality of first measurement patterns,each including a protruding pattern with a predetermined shape formed ofa resist film and a recessed pattern having a space with a shapecorresponding to the protruding pattern, the plurality of firstmeasurement patterns having different focus values at a time ofexposure, measuring edge inclination amounts of the protruding patternand the recessed pattern in the plurality of first measurement patterns,obtaining a focus dependence of the edge inclination amounts, which is acharacteristic showing how the edge inclination amounts vary withrespect to a variation in the focus value at the time of exposure, basedon correspondences between the measured edge inclination amounts and thefocus values, forming on a second substrate a second measurement patternincluding the protruding pattern and the recessed pattern atpredetermined focus values so as to measure edge inclination amounts ofthe protruding pattern and the recessed pattern in the secondmeasurement pattern, calculating a focus deviation amount deviating froma best focus at the time of exposure of the second measurement patternfrom the edge inclination amounts measured with respect to the secondmeasurement pattern based on the focus dependence of the edgeinclination amounts, and performing a pattern exposure with respect to aresist film on a third substrate at a focus value obtained by correctingthe calculated focus deviation amount. A dimension of the protrudingpattern and a dimension of the space of the recessed pattern are set tobe different so that best focus values at the time of exposing theprotruding pattern and the recessed pattern become closer.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are sectional views showing patterns for determining afocus deviation amount;

FIGS. 2A and 2B show variations in edge inclination amounts;

FIG. 3 shows a shift index with respect to a focus variation;

FIG. 4 is a flowchart showing a method for determining a focus deviationamount in a first embodiment;

FIG. 5 shows a focus dependence of a line pattern dimension;

FIG. 6 shows focus dependences of a top dimension and a bottom dimensionof the line pattern;

FIG. 7 shows a focus dependence of an edge inclination amount of theline pattern;

FIG. 8 shows focus dependences of a top dimension and a bottom dimensionof each of space patterns having different line widths;

FIG. 9 shows a focus dependence of an edge inclination amount of thespace pattern;

FIGS. 10A and 10B are drawings obtained by normalizing the edgeinclination amounts;

FIG. 11 shows focus dependences of the normalized edge inclinationamounts;

FIG. 12 shows a focus dependence of an optimal normalized edgeinclination amount;

FIG. 13 is a flowchart showing a method for determining a focusdeviation amount in a second embodiment;

FIGS. 14A and 14B are drawings for describing dimensional errors ofmasks;

FIG. 15 shows shift indexes of masks of individual types;

FIG. 16 shows a focus correction value with respect to the dimensionalerror of the mask;

FIG. 17 shows corrected shift indexes;

FIGS. 18A to 18F are sectional views showing steps of a pattern exposuremethod in a third embodiment;

FIGS. 19A and 19B are sectional views showing conventional patterns fordetermining a focus deviation amount;

FIGS. 20A and 20B show variations in conventional edge inclinationamounts; and

FIG. 21 shows a conventional model of a focus variation.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, the dimension of theprotruding pattern and the dimension of the space of the recessedpattern are made different so that the best focus values at the time ofexposing the respective patterns become closer, making it possible tosuppress the formation of the flat part near the best focus value in thecharacteristic combined with the focus dependence of the respective edgeinclination amounts. Consequently, a focus deviation amount also can bedetected near the best focus value.

In the method for determining a focus deviation amount or a patternexposure method according to the present invention, it is preferablethat normalized edge inclination amounts are obtained respectively forthe protruding pattern and the recessed pattern in the plurality offirst measurement patterns by subtracting values of the edge inclinationamounts at the best focus values from values of the edge inclinationamounts at the respective focus values, the normalized edge inclinationamounts obtained for the protruding pattern and the recessed pattern arecombined to prepare a shift index showing a correspondence with thefocus value at the time of exposure, and the shift index is used as thefocus dependence of the edge inclination amounts.

In this configuration, it is preferable that the shift index is modifiedby correcting a shift of the correspondence between the normalized edgeinclination amounts and the focus value at the time of exposure causedby a dimensional error of an exposure mask for forming the protrudingpattern and the recessed pattern with respect to a design value.

In the method for determining a focus deviation amount, the method forextracting a focus dependence of an edge inclination amount or thepattern exposure method according to the present invention, a linepattern formed of the resist film remaining in a linear form can be usedas the protruding pattern, and a space pattern having a space remainingafter removing the resist film in a linear form can be used as therecessed pattern.

Also, a dot pattern formed of the resist film remaining in a dotted formcan be used as the protruding pattern, and a hole pattern having a spaceremaining after removing the resist film in a dotted form can be used asthe recessed pattern.

Further, the edge inclination amounts can be measured by measuring a topdimension, which is a dimension at a top surface position of the resistfilm, and a bottom dimension, which is a dimension at a bottom surfaceposition thereof, and calculating a difference between the top dimensionand the bottom dimension for each of the protruding pattern and therecessed pattern.

Now, the principle of a method for determining a focus deviation amountused in the present invention will be described with reference to FIGS.1A, 1B, 2A, 2B and 3. FIGS. 1A and 1B are sectional views showing resistpatterns for determining a focus deviation amount. FIG. 1A shows anisolated line pattern 1. Lt denotes a top dimension of the line pattern1, namely, the length of a top surface. Lb denotes a bottom dimension ofthe line pattern 1, namely, the length of a bottom surface. The isolatedline pattern 1 is characterized in that a variation in itscross-sectional shape becomes notable when a focus value at the time ofexposure is shifted toward a positive side. FIG. 1B shows an isolatedspace pattern 2. St denotes a top dimension of the space pattern 2,namely, the length at the top of a space 3. Sb denotes a bottomdimension of the space pattern 2, namely, the length at the bottom ofthe space 3. The isolated space pattern 2 is characterized in that avariation in its cross-sectional shape becomes notable when the focusvalue at the time of exposure is shifted toward a negative side.

FIGS. 2A and 2B show variations in normalized edge inclination amounts.In FIGS. 2A and 2B, the horizontal axis indicates a focus value at thetime of exposing the patterns shown in FIGS. 1A and 1B, respectively.The vertical axis indicates a normalized edge inclination amount ΔLn ofthe line pattern 1 of FIG. 1A and a normalized edge inclination amountΔSn of the space pattern 2 of FIG. 1B, respectively. The normalized edgeinclination amounts ΔLn and ΔSn are values described below.

First, the edge inclination amount is defined as an amount showing adegree of inclination of end faces of each pattern. In the presentembodiment, edge inclination amounts ΔL and ΔS are expressedrespectively by the difference between the top dimension Lt and thebottom dimension Lb of the line pattern 1 of FIG. 1A and the differencebetween the top dimension St and the bottom dimension Sb of the spacepattern 2 of FIG. 1B (Equations (1) and (2)).ΔL=Lt−Lb  (1)ΔS=St−Sb  (2)

The normalized edge inclination amounts ΔLn and ΔSn respectively arevalues obtained by normalizing the edge inclination amounts ΔL and ΔSwhen exposed in a state where a focus is shifted with respect to edgeinclination amounts ΔLo and ΔSo at the time of exposure at the bestfocus value by using Equations (3) and (4).ΔLn=(ΔL−ΔLo)  (3)ΔSn=(ΔS−ΔSo)  (4)

As shown in FIG. 2A, in the line pattern, the normalized edgeinclination amount ΔLn varies considerably when the focus value isshifted toward the positive side. On the other hand, in the spacepattern, as shown in FIG. 2B, the normalized edge inclination amount ΔSnvaries considerably when the focus value is shifted toward the negativeside.

FIG. 3 shows the dependence of a shift index on a focus variation. Withits horizontal axis indicating a focus value and its vertical axisindicating a shift index SI, this figure shows a variation in the shiftindex SI with respect to the focus variation. Here, the shift index SIis represented by a calculation formula (Equation (5)) obtained byadding together the normalized edge inclination amounts ΔLn and ΔSn ofthe line pattern and the space pattern shown in FIGS. 2A and 2B.SI=ΔLn+ΔSn  (5)

The edge inclination amount ΔL of the line pattern varies when the focusvalue is on the positive side, and the edge inclination amount ΔS of thespace pattern varies when the focus value is on the negative side.Therefore, according to Equation (5), the shift index SI can bemonitored even when the focus value is shifted on the positive side orthe negative side.

In order to determine the focus deviation amount, the shift index SI iscalculated in advance by measuring an isolated line pattern and anisolated space pattern in a lot that has been subjected to exposure.With respect to a lot whose focus deviation amount is to be determined,a deviation amount of the focus value toward the positive side or thenegative side at the time of the exposure is calculated based on theobtained SI equation. In this way, it is possible to correct the focusvalue at the next lot exposure.

In the determination of the focus deviation amount based on theabove-described principle, the present invention has been made byimproving a method for preparing the shift index SI so that the focusdeviation amount near the best focus value can be determined moreaccurately.

The following is a detailed description of embodiments of the presentinvention, with reference to the accompanying drawings.

First Embodiment

The method for determining a focus deviation amount in the firstembodiment will be described with reference to FIGS. 4 to 9, 10A, 10B,11 and 12.

FIG. 4 is a flowchart showing the method according to the presentembodiment. Steps S1 to S7 show a method for extracting a focusdependence of an edge inclination amount expressed as the shift indexSI. Steps S8 to S10 show a method for forming resist patterns with whichthe focus deviation amount is to be determined and calculating the focusdeviation amount using the shift index SI. In the following, each of thesteps according to the present embodiment will be described.

Step S1

A best focus value Fo of the line pattern is determined. For thatpurpose, a CD—Focus characteristic, which is the relationship between aCD (critical dimension) and a focus value of an isolated line pattern,is determined. From this characteristic, the best focus value Fo isobtained.

First, plural kinds of line patterns are formed by exposures withdifferent focus values, and then the width of the formed patterns ismeasured. The line pattern used in the present embodiment is an isolatedline pattern with a width of 0.18 μm, which is equal to a minimumdimension of a device pattern (a design rule). FIG. 5 shows therelationship between the focus value and the pattern width obtained bythe measurement. In FIG. 5, the horizontal axis indicates the focusvalue at the time of exposure, and the vertical axis indicates the widthof the resist pattern of the 0.18 μm isolated line pattern. The focusvalue Fo when a curve 4 showing the CD—Focus characteristic shown inFIG. 5 is maximal is used as a best focus value. The width of anyportion of the resist pattern may be measured for obtaining thisCD—Focus characteristic as long as it is a fixed position of theisolated line pattern.

Step S2

As shown in FIG. 6, the CD—Focus characteristic of the top dimension Ltand the bottom dimension Lb of the line pattern is extracted. For thispurpose, plural kinds of line patterns are formed by exposures withdifferent focus values, and then the top dimension Lt and the bottomdimension Lb of the formed line patterns are measured. In FIG. 6, thehorizontal axis indicates the focus value, and the vertical axisindicates the dimensions of the formed line pattern. Curves 5 and 6respectively indicate the variation in the top dimension Lt and thebottom dimension Lb caused by a focus deviation. It can be seen that thedifference ΔL between the top dimension Lt and the bottom dimension Lbincreases on the positive side and hardly varies on the negative sidewith respect to the best focus value Fo of this line pattern.

Step S3 An edge inclination amount ΔL-Focus characteristic of the linepattern as shown in FIG. 7 is extracted. In FIG. 7, the horizontal axisindicates the focus value F, and the vertical axis indicates the edgeinclination amount ΔL(=Lt−Lb) of the line pattern. This FIG. 7 is madeusing measurement values shown in FIG. 6. In other words, the differencebetween the top dimension Lt and the bottom dimension Lb at the focusvalue F in FIG. 6 is obtained and expressed as the edge inclinationamount ΔL of the line pattern at the focus value F. The best focus valueFo calculated in FIG. 5 serves as a point of origin of the horizontalaxis of FIG. 7. Then, the edge inclination amount ΔL at each focus valueis calculated and plotted, thus forming a line 7 shown in FIG. 7.

As becomes evident from FIG. 7, when the focus value is on the negativeside, the edge inclination amount ΔL of the line pattern issubstantially constant. This is because, as shown in FIG. 6, the curve 5and the curve 6 tend to vary in a similar manner on the negative sidewith respect to the best focus value Fo. On the other hand, the curve 5falls more sharply than the curve 6 on the positive side with respect tothe best focus value Fo, so that ΔL increases as the focus value F movestoward the positive side.

Step S4

With respect to the isolated space pattern, the CD—Focus characteristicof the top dimension St and the bottom dimension Sb is extracted. Forthat purpose, a measurement is taken similarly to the case of extractingthe CD—Focus characteristic of the line pattern shown in FIG. 6.However, with respect to a 0.18 μm isolated line pattern, isolated spacepatterns with plural kinds of widths, for example, 0.20 μm, 0.25 μm and0.30 μm are produced for measurement.

This is for selecting the width of the space pattern finally so as tobring the best focus value of the space pattern close to the best focusvalue of the line pattern. In this manner, the problem in the currentresist that the best focus values of the line pattern and the spacepattern that have equal dimensions are different is avoided, therebyallowing the shift index SI to avoid staying flat near the best focusvalue.

FIG. 8 shows the result of the measurements for the space patterns withrespective widths. In FIG. 8, for a comparison with the focus value Foof the 0.18 μm isolated line pattern, Fo is set as the point of origin.The horizontal axis of FIG. 8 indicates a focus value, and the verticalaxis thereof indicates a variation in the top dimension St and thebottom dimension Sb caused by the focus deviation. A curve 8 in FIG. 8indicates the variation in the top dimension St of the isolated spacepattern with a width of 0.20 μm, and a curve 9 indicates the variationin the bottom dimension Sb of this space pattern. A curve 10 indicatesthe variation in the top dimension St of the isolated space pattern witha width of 0.25 μm, and a curve 11 indicates the variation in the bottomdimension Sb of this space pattern. A curve 12 indicates the variationin the top dimension St of the isolated space pattern with a width of0.30 μm, and a curve 13 indicates the variation in the bottom dimensionSb of this space pattern. Further, best focus values F₁, F₂ and F₃ ofthe space patterns with respective widths are shown in the figure. Theedge inclination amount ΔS, which is the difference between the topdimension St and the bottom dimension Sb, in the space pattern with eachwidth tends to show the focus dependence opposite to that of the edgeinclination amount ΔL in the line pattern. These curves rise on thenegative side with respect to their best focus values.

Step S5

Considering the relationship with respect to the best focus value of theline pattern, the width of the space pattern is set to differ from thewidth of the line pattern. In order to suppress the formation of theflat part in the shift index SI, it is desired that the space patternshould achieve the best focus value at the best focus value Fo of the0.18 μm line pattern. FIG. 8 indicates that the 0.25 μm space patternout of the space patterns with respective widths has the best focusvalue F₂ closest to the focus value Fo. Accordingly, it is appropriateto use the 0.25 μm space pattern. In the following steps, themeasurement value obtained from the 0.25 μm space pattern will be used.

Step S6

Similarly to the edge inclination amount ΔL-Focus characteristic of theline pattern shown in FIG. 7, the edge inclination amount ΔS-Focuscharacteristic of the space pattern is extracted as shown in FIG. 9. InFIG. 9, the horizontal axis indicates the focus value, and the verticalaxis indicates the edge inclination amount ΔS(=St−Sb). As shown in thisfigure, when the focus value is on the positive side, the edgeinclination amount ΔS of the space pattern is substantially constant.This is because, in FIG. 8, the curve 11 and the curve 10 tend to varyin a similar manner on the positive side with respect to the best focusvalue F2. On the other hand, the curve 11 falls more sharply than thecurve 10 on the negative side with respect to the best focus value F2,so that ΔS increases as the focus value F moves toward the negativeside.

Step S7

The shift index SI for obtaining the focus deviation amount is preparedbased on the edge inclination amounts ΔL and ΔS of the line pattern andthe space pattern.

First, as shown in FIG. 10A, data of the normalized edge inclinationamount ΔLn are formed from the edge inclination amount ΔL of the linepattern. In other words, from the line 7 indicating the focus dependenceof the edge inclination amount ΔL of the line pattern shown in FIG. 7obtained above, a line 15 shown in FIG. 10A is formed by shifting thepoint of origin to an edge inclination amount ΔLo at the best focusvalue Fo. That is to say, the line 7 of FIG. 7 is moved in parallel byΔLo along a Y-axis direction.

Also, as shown in FIG. 10B, data of the normalized edge inclinationamount ΔSn are formed from the edge inclination amount ΔS of the spacepattern. In other words, from the line 14 indicating the focusdependence of the edge inclination amount ΔS of the space pattern shownin FIG. 9, a line 16 shown in FIG. 10B is formed by shifting the pointof origin to an edge inclination amount ΔS2 at the best focus value F2.That is to say, the line 14 of FIG. 9 is moved in parallel by ΔS2 alongthe Y-axis direction.

Next, the line 15 in FIG. 10A and the line 16 in FIG. 10B that areformed as above are superposed so as to obtain a line 17 indicating theshift index SI in FIG. 11. FIG. 11 is a drawing showing the focusdependence of the normalized edge inclination amounts ΔLn and ΔSn. It isnoted that the line 7 in FIG. 7 and the line 14 in FIG. 9 also aresuperposed and shown in FIG. 11. The line 17 is formed of a line segment7 a of the line 7 located on the positive side of the focus and a linesegment 14 a of the line 14 located on the negative side of the focus.From a line segment 7 b and a line segment 14 b, the focus deviationcannot be detected because the edge inclination amount does not varyeven when the focus is shifted.

Here, in the line 17 in FIG. 11, a flat part remains in a portionextending from the point of origin Fo toward the focus value F2 on thenegative side. This is because the best focus value F2 of the spacepattern does not completely match with the best focus value Fo of theline pattern. As this difference between Fo and F2 becomes smaller, thecorrection can be carried out more accurately. A straight line 18 shownin FIG. 12 indicates the focus dependence of an optimal normalized edgeinclination amount passing through Fo. It is desired that the shiftindex SI should be adjusted to be as close as possible to this straightline 18.

It is desirable that the difference between the best focus values Fo andF2 should be set to be within 0.2 μm practically. It is furtherpreferable that the dimensional relationship between the line patternand the space pattern is set so that the difference is within 0.1 μm.This range indicates a range in which, by correcting the focus deviationamount based on the formed shift index SI, a resist pattern havingpractically favorable shape and dimension can be formed.

As described above, the shift index SI showing the focus dependence ofthe edge inclination amount is formed so that its accuracy near the bestfocus is enhanced. Based on this shift index SI, it becomes possible todetermine the focus deviation amount accurately. The following stepsshow the method for determining the focus deviation amount at the timeof exposure based on the shift index SI formed in the steps describedabove.

Step S8

In an exposure step in which the focus deviation amount is to bedetermined, measurement patterns for determining a focus deviationamount are formed on a semiconductor substrate to be processed. As themeasurement patterns, the isolated line pattern and the isolated spacepattern shown in FIGS. 1A and 1B respectively are formed.

Step S9

With respect to the formed measurement patterns, the top dimension Ltand the bottom dimension Lb of the line pattern and the top dimension Stand the bottom dimension Sb of the space pattern are measured. Using thetop dimensions Lt and St and bottom dimensions Lb and Sb that have beenmeasured, the edge inclination amount ΔL of the line pattern and theedge inclination amount ΔS of the space pattern are calculated.Subsequently, by subtracting the edge inclination amount ΔLo at the bestfocus value Fo shown in FIG. 7 from the edge inclination amount ΔL ofthe line pattern, the normalized edge inclination amount ΔLn isobtained. By subtracting the edge inclination amount ΔS2 at the bestfocus value F2 shown in FIG. 9 from the edge inclination amount ΔS ofthe space pattern, the normalized edge inclination amount ΔSn isobtained. Then, the normalized edge inclination amount ΔLn of the linepattern and the normalized edge inclination amount ΔSn of the spacepattern are added together, thereby obtaining an SI value of thepatterns formed on the semiconductor substrate (Equation (5)).

Step S10

The thus obtained shift index value SI is compared with the verticalaxis of the SI chart shown in FIG. 12, thereby obtaining the focus valueon the horizontal axis corresponding to this SI value. This focus valueon the horizontal axis is a focus deviation amount Δfocus.

By correcting this focus deviation amount Δfocus at the next exposure,exposure always can be conducted with the best focus value, making itpossible to form a resist pattern with a small dimensional variation andan excellent shape.

Second Embodiment

The method for determining a focus deviation amount in the secondembodiment will be described with reference to FIGS. 12, 13, 14A, 14B,15 to 17.

FIG. 13 is a flowchart showing a main part of the method according tothe present embodiment. The method according to the present embodimenthas Steps S11 to S14 in the flowchart of FIG. 13 between Steps S1 to S7and Steps S8 to S10 shown in FIG. 4. This method is characterized bycorrecting the influence of production errors of masks used for patternexposure for the purpose of eliminating or reducing the flat part of theline 17 shown in FIG. 11.

FIGS. 14A and 14B are drawings for describing dimensional errors inmanufacturing masks. Ld denotes a design dimension of the mask for theline pattern, and Sd denotes a design dimension of the mask for thespace pattern. Lm denotes a measurement value of a finished dimension onthe manufactured masks for the line pattern, and Sm denotes that for thespace pattern. The dimensional errors of the masks are (Lm−Ld) and(Sm−Sd), respectively.

In the case where a mask dimensional error 19 is 0.005 μm, for example,the finished dimension Lm of a line pattern 20 shown in FIG. 14A becomeswider by 0.01 μm so as to be a line pattern 20 a indicated by brokenlines. The best focus of this line pattern 20 a is shown as F_(L) inFIG. 12. Also, the finished dimension Sm of a space pattern 21 shown inFIG. 14B becomes narrower by 0.01 μm so as to be a space pattern 21 aindicated by broken lines. In this case, the best focus of the spacepattern 21 a is shown as F_(S) in FIG. 12. Owing to this deviation oftheir best focuses, the straight line 18 becomes a line 22. In thiscase, with respect to a normalized edge inclination amount at a giventime of exposure, the focus deviation amount is Δf₁ according to theshift index shown by the straight line 18, whereas it is Δf₂, which isdifferent from Δf₁, according to that shown by the line 22.

In this way, even if the design rule of the line pattern and the spacepattern that achieves an equal best focus value is determined by theflow shown in FIG. 4 before manufacturing masks, the dimensional error19 during the mask manufacture causes the best focus values of the linepattern and the space pattern to be different as shown in FIG. 12. As aresult, the flat part is formed, so that the shift index SI capable ofmaking an accurate correction cannot be obtained.

Thus, according to Steps S11 to S14, based on the sum of the maskdimensional error for the line pattern and that of the space pattern, afocus correction value for suppressing the influence of the maskdimensional error is calculated as follows.

Step S11

First, for each type, a shift index SI for extracting a characteristiccorresponding to the error is obtained. The method therefor is asfollows: according to Steps S1 to S7 shown in FIG. 4, a mask formed foreach type is used for exposure at a plurality of focus values, and thenthe shift index SI is obtained in a manner similar to that describedabove. As an example, FIG. 15 shows altogether the shift indexes SIobtained using masks A to D for four types. From this figure, it can beseen that the line of SI is shifted along an X-axis direction due to thedimensional error of the mask of each type.

Step S12

The dimensional errors of the masks used in Step S11 are calculated.First, a mask dimensional error ΔML of the line pattern and a maskdimensional error ΔMS of the space pattern are calculated from thedesign dimensions Ld and Sd of the masks and the finished dimensions Lmand Sm on the manufactured masks shown in FIGS. 14A and 14B (Equations(6) and (7)).ΔML=Lm−Ld  (6)ΔMS=Sm−Sd  (7)

Then, a mask dimensional error ΔMe is expressed by the sum of the maskdimensional error ΔML of the line pattern and the mask dimensional errorΔMS of the space pattern (Equation (8)).ΔMe=ΔML+ΔMS  (8)

As shown in FIG. 15, the mask dimensional error ΔMe of each type causesa difference in the shift indexes SI. Owing to this difference in theshift indexes SI, the focus deviation amounts calculated from the shiftindexes SI differ from each other. Thus, it is necessary to correct thefocus deviation amount with respect to the mask dimensional error ΔMe.

Step S13

The calculated value of the mask dimensional error ΔMe is used to make agraph showing a mask dimensional error ΔMe-focus correction valuecharacteristic.

In order to obtain a correction value of the focus deviation amount withrespect to the mask dimensional error ΔMe, a focus correction valueΔFmask is calculated based on the values of the mask dimensional errorsΔMe of the masks A to D and the shift indexes SI obtained for thesemasks. FIG. 16 shows the characteristic of the focus correction valueΔFmask with respect to the mask dimensional error ΔMe that has beenextracted from the measurement values for the masks A to D. Thehorizontal axis indicates the mask dimensional error, and the verticalaxis indicates the focus correction value ΔFmask.

Step S14

The shift index SI in which the mask dimensional error is corrected isformed for each type. First, the mask dimensional error ΔMe iscalculated for each type. Then, based on the characteristic of the focuscorrection value ΔFmask shown in FIG. 16, the calculated maskdimensional error ΔMe is used for obtaining a focus deviation amountcorrection value ΔFmask specific for each type. Thereafter, a straightline 23, which is a shift index passing through the point of origin,shown in FIG. 17 is shifted by ΔFmask along the X direction, therebyforming corrected shift indexes SI for the respective types (masks E toH).

By providing feedback on the final correction value from the correctedshift index SI formed for each type as described above to the conditionfor exposure, it becomes possible to carry out still more accurate focuscorrection.

Third Embodiment

The pattern exposure method according to the third embodiment will bedescribed referring to FIGS. 18A to 18F, which are sectional viewsshowing steps thereof The exposure method according to the presentembodiment is a method for forming a resist pattern with a smalldimensional variation and an excellent shape by using the shift index SIdetermined by the method described in the above embodiments.

First, as shown in FIG. 18A, a pattern exposure is carried out for aresist film 31 formed on a first semiconductor substrate 30. A mask 32 afor exposure is provided with an isolated line pattern 33 and anisolated space pattern 34 for determining a focus deviation amount. Theexposure using this mask 32 a followed by development forms a firstmeasurement pattern 37 including an isolated line pattern 35 and anisolated space pattern 36 shown in FIG. 18B.

Although this figure illustrates only one set of the measurement pattern37, plural sets of the measurement patterns 37 are formed in practice bycarrying out the exposure with plural focus values as data shown inFIGS. 2A and 2B. For example, by carrying out the exposure with elevenfocus values from −0.5 μm to +0.5 μm with a pitch of 0.1 μm, eleven setsof the measurement patterns are formed. These first measurement patterns37 may be formed on a single semiconductor substrate or pluralsemiconductor substrates.

Next, the first measurement pattern 37 is measured, thus making the SIchart as shown in FIG. 11 by the method described in the aboveembodiments.

Subsequently, as shown in FIG. 18C, pattern exposure is carried out fora resist film 39 formed on a second semiconductor substrate 38 with apredetermined focus value. A mask 32 b for exposure is provided with theisolated line pattern 33 and the isolated space pattern 34 fordetermining a focus deviation amount. The development thereafter forms asecond measurement pattern 42 including an isolated line pattern 40 andan isolated space pattern 41 as shown in FIG. 18D. The measurementpattern is formed in this step for the purpose of monitoring a slightdeviation of the focus value at the time of exposure caused by a processvariation by using the SI chart.

Next, the top dimensions Lt and St and the bottom dimensions Lb and Sbof the line pattern 40 and the space pattern 41 are measured.Subsequently, using the top dimensions Lt and St and the bottomdimensions Lb and Sb, the edge inclination amount ΔL of the line patternand the edge inclination amount ΔS of the space pattern are calculated.Then, as described referring to FIGS. 10A and 10B, these edgeinclination amounts are normalized to obtain ΔLn and ΔSn. Thereafter,the SI value is calculated.

Next, by the method illustrated by FIG. 12, from the resultant SI valueand the SI chart made in the above-described step, a deviation amountΔfocus from a desired focus at the time of exposure in this step iscalculated.

Thereafter, the obtained deviation amount Δfocus of the focus value isused to make the correction at the time of setting the focus for thenext exposure. In other words, as shown in FIG. 18E, a pattern exposurewith the corrected focus value is carried out for a resist film 44formed on a third semiconductor substrate 43. In this step, a mask 32 cfor exposure also is provided with the isolated line pattern 33 and theisolated space pattern 34 for determining a focus deviation amount. Thedevelopment thereafter forms a third measurement pattern 47 including anisolated line pattern 45 and an isolated space pattern 46 as shown inFIG. 18F. Similarly to the previous step, the measurement pattern isformed in this step for the purpose of monitoring a slight deviation ofthe focus value at the time of exposure caused by a process variation byusing the SI chart. By measuring the edge inclination amount of themeasurement pattern 47, it is possible to calculate the focus deviationamount, thus suppressing the focus deviation at the next exposure.

Although the width of the space pattern has been adjusted so that thebest focus value of the space pattern is brought closer to the bestfocus value of the line pattern with a desired line width in theembodiments described above, the adjustment also can be made in areversed manner. In other words, the line width of the line pattern alsomay be adjusted so that the best focus value of the line pattern isbrought closer to the best focus value of the space pattern with adesired width.

Furthermore, a configuration similar to that described above also may beachieved by using one or more dot patterns instead of the line patternand using one or more hole patterns instead of the space pattern. Thisis because the dot pattern and the hole pattern vary in their topdimension and bottom dimension with the focus variation regardless ofthe pattern density, making it possible to monitor the focus deviation.In this case, the top dimension and the bottom dimension of the dotpattern and the hole pattern may be the dimension of their diameter, forexample.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to raise the accuracyof determining the focus deviation amount in pattern exposure inlithography, thereby forming a minute resist pattern accurately.

1. A method for determining a focus deviation amount, comprising:forming on a first substrate a plurality of first measurement patterns,each including a protruding pattern with a predetermined shape formed ofa resist film and a recessed pattern having adjacent patterns of theresist film with a space provided therebetween, the plurality of firstmeasurement patterns having different focus values at a time ofexposure; measuring edge inclination amounts of the protruding patternand the recessed pattern in the plurality of first measurement patterns;obtaining a focus dependence of the edge inclination amounts, which is acharacteristic showing how the edge inclination amounts vary withrespect to a variation in the focus value at the time of exposure, basedon correspondences between the measured edge inclination amounts and thefocus values; forming on a second substrate a second measurement patternincluding the protruding pattern and the recessed pattern so as tomeasure edge inclination amounts of the protruding pattern and therecessed pattern in the second measurement pattern; and calculating afocus deviation amount deviating from a best focus at the time ofexposure of the second measurement pattern from the edge inclinationamounts measured with respect to the second measurement pattern based onthe focus dependence of the edge inclination amounts; wherein a designvalue of a width of the predetermined shape of the protruding patternand a design value of a width of the space of the recessed pattern areset so that best focus values at the time of exposing the protrudingpattern and the recessed pattern become closer.
 2. The method fordetermining a focus deviation amount according to claim 1, whereinnormalized edge inclination amounts are obtained respectively for theprotruding pattern and the recessed pattern in the plurality of firstmeasurement patterns by subtracting values of the edge inclinationamounts at the best focus values from values of the edge inclinationamounts at the respective focus values, the normalized edge inclinationamounts obtained for the protruding pattern and the recessed pattern arecombined to prepare a shift index showing a correspondence with thefocus value at the time of exposure, and the shift index is used as thefocus dependence of the edge inclination amounts.
 3. The method fordetermining a focus deviation amount according to claim 2, wherein theshift index is modified by correcting a shift of the correspondencebetween the normalized edge inclination amounts and the focus value atthe time of exposure caused by a dimensional error of an exposure maskfor forming the protruding pattern and the recessed pattern with respectto a design value.
 4. The method for determining a focus deviationamount according to claim 1, wherein a line pattern formed of the resistfilm remaining in a linear form is used as the protruding pattern, and aspace pattern having a space remaining after removing the resist film ina linear form is used as the recessed pattern.
 5. The method fordetermining a focus deviation amount according to claim 1, wherein a dotpattern formed of the resist film remaining in a dotted form is used asthe protruding pattern, and a hole pattern having a space remainingafter removing the resist film in a dotted form is used as the recessedpattern.
 6. The method for determining a focus deviation amountaccording to claim 1, wherein the edge inclination amounts are measuredby measuring a top dimension, which is a dimension at a top surfaceposition of the resist film, and a bottom dimension, which is adimension at a bottom surface position thereof, and calculating adifference between the top dimension and the bottom dimension for eachof the protruding pattern and the recessed pattern.
 7. The method fordetermining a focus deviation amount according to claim 1, wherein adimensional relationship between the protruding pattern and the recessedpattern is set so that the difference between the best focus values atthe time of exposing the protruding pattern and the recessed pattern iswithin 0.2 μm.
 8. The method for determining a focus deviation amountaccording to claim 7, wherein the dimensional relationship between theprotruding pattern and the recessed pattern is set so that thedifference between the best focus values at the time of exposing theprotruding pattern and the recessed pattern is within 0.1 μm.
 9. Amethod for extracting a focus dependence of an edge inclination amount,comprising: forming on a substrate a plurality of measurement patterns,each including a protruding pattern with a predetermined shape formed ofa resist film and a recessed pattern having adjacent patterns of theresist film a space provided therebetween, the plurality of measurementpatterns having different focus values at a time of exposure; measuringedge inclination amounts of the protruding pattern and the recessedpattern in the plurality of measurement patterns; and obtaining a focusdependence of the edge inclination amounts, which is a characteristicshowing how the edge inclination amounts vary with respect to avariation in the focus value at the time of exposure, based oncorrespondences between the measured edge inclination amounts and thefocus values; wherein a design value of a width of the predeterminedshape of the protruding pattern and a design value of a width of thespace of the recessed pattern are set so that best focus values at thetime of exposing the protruding pattern and the recessed pattern becomecloser.
 10. The method for extracting a focus dependence of an edgeinclination amount according to claim 9, wherein a line pattern formedof the resist film remaining in a linear form is used as the protrudingpattern, and a space pattern having a space remaining after removing theresist film in a linear form is used as the recessed pattern.
 11. Themethod for extracting a focus dependence of an edge inclination amountaccording to claim 9, wherein a dot pattern formed of the resist filmremaining in a dotted form is used as the protruding pattern, and a holepattern having a space remaining after removing the resist film in adotted form is used as the recessed pattern.
 12. The method forextracting a focus dependence of an edge inclination amount according toclaim 9, wherein the edge inclination amounts are measured by measuringa top dimension, which is a dimension at a top surface position of theresist film, and a bottom dimension, which is a dimension at a bottomsurface position thereof, and calculating a difference between the topdimension and the bottom dimension for each of the protruding patternand the recessed pattern.
 13. The method for extracting a focusdependence of an edge inclination amount according to claim 9, wherein adimensional relationship between the protruding pattern and the recessedpattern is set so that the difference between the best focus values atthe time of exposing the protruding pattern and the recessed pattern iswithin 0.2 μm.
 14. The method for extracting a focus dependence of anedge inclination amount according to claim 13, wherein the dimensionalrelationship between the protruding pattern and the recessed pattern isset so that the difference between the best focus values at the time ofexposing the protruding pattern and the recessed pattern is within 0.1μm.
 15. A pattern exposure method, comprising: forming on a firstsubstrate a plurality of first measurement patterns, each including aprotruding pattern with a predetermined shape formed of a resist filmand a recessed pattern having adjacent patterns of the resist film witha space provided therebetween, the plurality of first measurementpatterns having different focus values at a time of exposure; measuringedge inclination amounts of the protruding pattern and the recessedpattern in the plurality of first measurement patterns; obtaining afocus dependence of the edge inclination amounts, which is acharacteristic showing how the edge inclination amounts vary withrespect to a variation in the focus value at the time of exposure, basedon correspondences between the measured edge inclination amounts and thefocus values; forming on a second substrate a second measurement patternincluding the protruding pattern and the recessed pattern atpredetermined focus values so as to measure edge inclination amounts ofthe protruding pattern and the recessed pattern in the secondmeasurement pattern; calculating a focus deviation amount deviating froma best focus at the time of exposure of the second measurement patternfrom the edge inclination amounts measured with respect to the secondmeasurement pattern based on the focus dependence of the edgeinclination amounts; and performing a pattern exposure with respect to aresist film on a third substrate at a focus value obtained by correctingthe calculated focus deviation amount; wherein a design value of a widthof the predetermined shape of the protruding pattern and a design valueof a width of the space of the recessed pattern are set so that bestfocus values at the time of exposing the protruding pattern and therecessed pattern become closer.
 16. The pattern exposure methodaccording to claim 15, wherein normalized edge inclination amounts areobtained respectively for the protruding pattern and the recessedpattern in the plurality of first measurement patterns by subtractingvalues of the edge inclination amounts at the best focus values fromvalues of the edge inclination amounts at the respective focus values,the normalized edge inclination amounts obtained for the protrudingpattern and the recessed pattern are combined to prepare a shift indexshowing a correspondence with the focus value at the time of exposure,and the shift index is used as the focus dependence of the edgeinclination amounts.
 17. The pattern exposure method according to claim16, wherein the shift index is modified by correcting a shift of thecorrespondence between the normalized edge inclination amounts and thefocus value at the time of exposure caused by a dimensional error of anexposure mask for forming the protruding pattern and the recessedpattern with respect to a design value.
 18. The pattern exposure methodaccording to claim 15, wherein a line pattern formed of the resist filmremaining in a linear form is used as the protruding pattern, and aspace pattern having a space remaining after removing the resist film ina linear form is used as the recessed pattern.
 19. The pattern exposuremethod according to claim 15, wherein a dot pattern formed of the resistfilm remaining in a dotted form is used as the protruding pattern, and ahole pattern having a space remaining after removing the resist film ina dotted form is used as the recessed pattern.
 20. The pattern exposuremethod according to claim 15, wherein the edge inclination amounts aremeasured by measuring a top dimension, which is a dimension at a topsurface position of the resist film, and a bottom dimension, which is adimension at a bottom surface position thereof, and calculating adifference between the top dimension and the bottom dimension for eachof the protruding pattern and the recessed pattern.
 21. The patternexposure method according to claim 15, wherein a dimensionalrelationship between the protruding pattern and the recessed pattern isset so that the difference between the best focus values at the time ofexposing the protruding pattern and the recessed pattern is within 0.2μm.
 22. The pattern exposure method according to claim 21, wherein thedimensional relationship between the protruding pattern and the recessedpattern is set so that the difference between the best focus values atthe time of exposing the protruding pattern and the recessed pattern iswithin 0.1 μm.